1. Field of the Invention
This invention relates to photographic objectives of a wide image angle while still reducing the size by shortening the total length of the lens system, or the distance from the lens system's 1st lens surface to the focal plane.
2. Description of the Prior Art
Recently, as minimization of the bulk and size of cameras advances, there is an increasing demand for compact objective lenses in which the total length of the lens system is reduced. In order to reduce the total length of the lens system below the focal length, it is desirable to construct the lens system from a front group of positive power and a rear group of negative power. Such power distribution has found many uses in long focal length lenses but is seldom applied to wide angle lenses of 60.degree. or more with increased relative apertures and short total lengths of the lens systems.
With this kind of power distribution, as the total length shortens, as the relative aperture increases, as the image angle widens, distortion and astigmatism, or comatic aberration and halo objectionably increase.
For example, Japanese Pat. No. 44-10831 discloses a lens system of such power distribution, but the specific objective described there has an angular field of 46.degree., which belongs to the category of standard objectives and calls for an increase in the astigmatic difference when there is an increase in the image angle. Also shown in Japanese Pat. No. 52-48011 is an objective which has, however, an F-number of 1:4.5. This speed is not sufficiently fast.